The present invention relates to a failure (improper-state) detection apparatus for a resolver configured to output a sine signal indicative of sin θ and a cosine signal indicative of cos θ according to rotational angle θ of a rotator.
Japanese Patent Application Publication No. H09 (1997)-72758 discloses a previously-proposed failure detection apparatus for a resolver. In this technique, a value of sin2 θ+cos2 θ is calculated based on the sine and cosine signals, and it is decided that the resolver has caused a failure when the value of sin2 θ+cos2 θ deviates from a predetermined normal range.